Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Mapping the optimal route between 2 quantum states

31.07.2014

Experiment measures millions of quantum trajectories to predict 'most likely' route

As a quantum state collapses from a quantum superposition to a classical state or a different superposition, it will follow a path known as a quantum trajectory. For each start and end state there is an optimal or "most likely" path, but it is not as easy to predict the path or track it experimentally as a straight-line between two points would be in our everyday, classical world.


Measurement data showing the comparison with the 'most likely' path (in red) between initial and final quantum states (black dots). The measurements are shown on a representation referred to as a Bloch sphere.

Credit: Areeya Chantasri

In a new paper featured this week on the cover of Nature, scientists from the University of Rochester, University of California at Berkeley and Washington University in St. Louis have shown that it is possible to track these quantum trajectories and compare them to a recently developed theory for predicting the most likely path a system will take between two states.

Andrew N. Jordan, professor of physics at the University of Rochester and one of the authors of the paper, and his group had developed this new theory in an earlier paper. The results published this week show good agreement between theory and experiment.

For their experiment, the Berkeley and Washington University teams devised a superconducting qubit with exceptional coherence properties, permitting it to remain in a quantum superposition during the continuous monitoring. The experiment actually exploited the fact that any measurement will perturb a quantum system. This means that the optimal path will come about as a result of the continuous measurement and how the system is being driven from one quantum state to another.

Kater Murch, co-author and assistant professor at Washington University in St. Louis, explained that a key part of the experiment was being able to measure each of these trajectories while the system was changing, something that had not been possible until now.

Jordan compares the experiment to watching butterflies make their way one by one from a cage to nearby trees. "Each butterfly's path is like a single run of the experiment," said Jordan. "They are all starting from the same cage, the initial state, and ending in one of the trees, each being a different end state." By watching the quantum equivalent of a million butterflies make the journey from cage to tree, the researchers were in effect able to predict the most likely path a butterfly took by observing which tree it landed on (known as post-selection in quantum physics measurements), despite the presence of a wind, or any disturbance that affects how it flies (which is similar to the effect measuring has on the system).

"The experiment demonstrates that for any choice of final quantum state, the most likely or 'optimal path' connecting them in a given time can be found and predicted," said Jordan. "This verifies the theory and opens the way for active quantum control techniques." He explained that only if you know the most likely path is it possible to set up the system to be in the desired state at a specific time.

About the University of Rochester

The University of Rochester is one of the nation's leading private universities. Located in Rochester, N.Y., the University gives students exceptional opportunities for interdisciplinary study and close collaboration with faculty through its unique cluster-based curriculum. Its College, School of Arts and Sciences, and Hajim School of Engineering and Applied Sciences are complemented by its Eastman School of Music, Simon School of Business, Warner School of Education, Laboratory for Laser Energetics, School of Medicine and Dentistry, School of Nursing, Eastman Institute for Oral Health, and the Memorial Art Gallery.

David Barnstone | Eurek Alert!

Further reports about: Mapping choice measurement physics quantum state quantum trajectory

More articles from Physics and Astronomy:

nachricht Four elements make 2-D optical platform
26.09.2017 | Rice University

nachricht The material that obscures supermassive black holes
26.09.2017 | Instituto de Astrofísica de Canarias (IAC)

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: The fastest light-driven current source

Controlling electronic current is essential to modern electronics, as data and signals are transferred by streams of electrons which are controlled at high speed. Demands on transmission speeds are also increasing as technology develops. Scientists from the Chair of Laser Physics and the Chair of Applied Physics at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have succeeded in switching on a current with a desired direction in graphene using a single laser pulse within a femtosecond ¬¬ – a femtosecond corresponds to the millionth part of a billionth of a second. This is more than a thousand times faster compared to the most efficient transistors today.

Graphene is up to the job

Im Focus: LaserTAB: More efficient and precise contacts thanks to human-robot collaboration

At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.

Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Nerves control the body’s bacterial community

26.09.2017 | Life Sciences

Four elements make 2-D optical platform

26.09.2017 | Physics and Astronomy

Goodbye, login. Hello, heart scan

26.09.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>